Combined Sewer Overflow

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Public Information
The City of Bloomington has an NPDES Permit to operate several CSO's (Combined Sewer Overflows). A copy of a draft reissued NPDES permit to discharge into waters of the state is available here. If you wish to comment on the draft permit, please do so within 30 days of the Public Notice date. Please check this website periodically for updates regarding this important matter.

Combined sewers have both sanitary and storm water running through them. Under federal mandate, the City spends millions to separate the sewers. Here are reports on the effort to manage and eliminate Combined Sewer Overflow.

Combined Sewer Overflow Reporting Procedures

BNWD Long-Term CSO Control Plan, April 2003

BNWD Long-Term CSO Control Plan, Addendum 1

CSO Pollution Prevention Plan

CSO Operational Plan

Please contact the Engineering Department at to make further inquiries regarding this matter.

Combined Sewer Overflow in the Twin Cities
The City of Bloomington, in conjunction with the Town of Normal and the Bloomington and Normal Water Reclamation District (BNWRD), own and maintain three types of sewers within the Bloomington - Normal area. These include storm sewers, sanitary sewers and combined sewer systems. Many people are aware of the purpose of the storm and sanitary sewer systems, but are not familiar with combined sewer systems.

A combined sewer system is a system in which both the runoff generated by melting snow or rains AND sanitary waste water flow through the same pipe. This system generally carries sanitary waste during periods of dry weather, but carries both sanitary waste and the runoff from melting snow or rainwater as these weather situations occur. The combined sewer system is designed to handle most typical rain and snow events, but becomes overloaded during periods of heavy rainfall or sudden downpours. It is during these heavy rains and sudden downpours when the combined sewer overflows (CSOs) operate. A combined sewer overflow is an event which occurs when a combined sewer exceeds its capacity and begins to discharge excess water into a nearby receiving water. The combined sewers within the City of Bloomington are located north of Veteran’s Parkway and West of Mercer Avenue. However, some of the storm and sanitary sewers outside of this area flow into main trunk sewers within this area, thus contributing to the combined sewer system. The City of Bloomington currently monitors 4 combined sewer overflow locations on a daily basis.

Combined sewers are not a new concept. Municipalities nationwide began using combined sewers in the early 1800’s. They were built until the 1960’s when the United States Environmental Protection Agency (U.S. EPA) began requiring new sewer installations to be separated, i.e., storm water would only enter the storm sewer system and sanitary waste would only enter the sanitary sewer system.

The Clean Water Act
The passage of the Clean Water Act in 1972 led to the U. S. EPA prohibiting CSOs and required municipalities to eliminate them unless an economic hardship could be proven by said municipality. The BNWRD facility requested a waiver of this requirement based upon economic hardship in 1983 as it was estimated the cost to comply with this mandate would be roughly $40 million. BNWRD began implementing phased changes to the West Oakland Avenue plant as part of the agreement with the U.S. EPA.

 The U. S. EPA implemented 9 minimum control measures for Combined Sewer Overflows in 1996. These measures are as follows:

  1. Proper operation and regular maintenance programs for the sewer system and CSO outfalls;
  2. Maximum use of the collection system for storage;
  3. Review and modification of pretreatment requirements to ensure that CSO impacts are minimized;
  4. Maximization of flow to the Publicly Owned Treatment Works (POTW) for treatment;
  5. Elimination of CSOs during dry weather;
  6. Control of solid and floatable materials in CSOs;
  7. Pollution prevention programs to reduce contaminants in CSOs;
  8. Public notification to ensure that the public receives adequate notification of CSO occurrences and impacts;
  9. Monitoring to effectively characterize CSO impacts and the efficacy of CSO controls.

The U. S. EPA also required entities that have CSOs to implement a Long Term CSO Control Plan. The BNWRD staff created Illinois’ first Long Term CSO Control Plan to be approved by the U. S. EPA.

Sanitary Sewer and Storm Water Funding in Bloomington
The funding of sewer system maintenance and improvements is through charges on the water bill. There are separate sewer charges for the City Sewer System which conveys the sewage and the BNWRD treatment of the sewage. Increases in the rates for the sewer charges are established independently. The City utilizes a sewer rate study to determine what the rates should be. The last rate study for sewer was completed in 2008 and can be found here.

Citizen's Advisory Committee
A Citizen's Advisory Committee was created to help discuss combined sewers, their overflows and their impact on the local environment. This committee is comprised of volunteers from the following entities:

1. Bloomington and Normal Water Reclamation District (BNWRD)
2. McLean County
3. McLean County Regional Planning Commission
4. Town of Normal
5. City of Bloomington
6. Illinois Wesleyan University
7. Illinois State University
8. Ecology Action Center
9. Unit 5 Schools
10. John Wesley Powell Audubon Chapter
11. League of Women Voters
12. McLean County Soil & Water Conservation District

This committee will meet on a quarterly basis at a date and time to be scheduled. Please check this website periodically for updates regarding this important matter.

Please contact the Engineering Department at to make further inquiries regarding this matter.

To report a storm water, sanitary sewer, or water issue, call 309-434-2225 during regular office hours. For emergency issues (i.e. backup, illicit discharge, unreported water main break) after hours, call 309-820-8888.

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